Investigating Collections: Science Meets Archaeology at the Library of Congress

This post is about research conducted by the author, in conjunction with Dr. Tana Villafana, Research Chemist and Spectroscopist, from the Preservation Research and Testing Division, and with Rosemary Ryan, Archaeological Research Fellow, at the Library of Congress. The research is part of a larger project to characterize and study all of the Mesoamerican jade and green stone objects that are part of the Jay I. Kislak Collection of the Archaeology and History of the Early Americas at the Library.

Several months ago the Library of Congress began an investigation of a small green stone bead that, along with may other jade and green stone objects, is part of the Jay I. Kislak Collection of the Archaeology of the Early Americas. This small bead, made from a low quality jade or other green stone, was donated to the Library by Jim May, a long time member of the Institute of Maya Studies, who received the bead many decades ago from the late Lister Witherspoon IV, a one time director of the Institute. The bead itself is fairly common, and typical of beads found in the archaeological record throughout Mesoamerica.

What is unique about this particular bead, however, is what it contains. Still attached to the inside of the bead, after perhaps more than 2,000 years, was a small fragment of what appeared to be the cord or twine that was used to suspend it around the neck of an ancient Maya, Nahua, or Olmec noble. Organic material, like twine, is a rare find in Mesoamerican archaeology, where the damp and humid environments are not conducive to the survival of organic material such as cord, cloth, or wood.

Jade of any kind was revered by the Olmec, the Maya, and other Mesoamerican cultures and a significant variety of carved objects made from it and lesser green stones, like serpentine, have been found in archaeological context throughout Mexico and Central America. These include human figures, celts and axes, and personal ornaments like ear flares, necklaces, and beads, such as the one being investigated here.

Because of the rarity of the cord fragments found in this particular bead, the author, in conjunction with scientists from the Preservation Research and Testing Division at the Library of Congress, decided to undertake an investigation using Scanning Electron Microscopy (SEM) and Energy Dispersive X-ray Spectroscopy (EDX) to search for clues to the makeup of the cord fragments. These two techniques were selected because they can be performed on rare and fragile objects non-destructively, and in this case, without researchers disturbing the cord fragments or having to remove them from inside the bead.

The preliminary results of the investigations have found that the fiber within the bead seems to come from a species of Agave plant. Agave fibers like those shown in the SEM photograph below, have been used to make rope and twine in Southern Mexico for centuries, with most of the modern ropes and twines coming from the Agave sisalana species, which is sometimes referred to as “sisal hemp.” Looking closely at the SEM images of the cord fragment, magnified nearly two-thousand times, one can see both the cell walls of the plant and cross-sectional structure of the fibers themselves.

EDX is an analytical technique that allows for the determination of the elemental composition of anything on the surface of an object that is excited by a high-energy particle beam, like the electrons in a scanning electron microscope. Using the EDX technique, a map was made to determine the chemical elements on the surface of the bead and the cord fragments, to determine if it might reveal hints of the kinds of dirt and other detritus that can also be seen in the SEM images.

The map in the figure below is a scanning electron microscope image that is color-coded with the EDX results to show the chemical elements on the surface of the cord fragment. From the map, it is easy to see, in green, the carbon that makes up the plant fibers. The particles on the cord and bead seem to be lime (in the form of calcium oxide) and iron (most likely from red hemitate, a form of iron oxide). Both lime and iron are common in the kind of archaeological context one would expect this kind of bead to be found in.

Although none of the results discussed above are as of yet definitive, as research will continue through the coming months, they are presented here to give readers just a small taste of how science meets archaeology at the Library of Congress.